On Tue, Jul 21, 2009 at 07:25:58AM -0400, Chad Mynhier wrote:
> On Tue, Jul 21, 2009 at 2:52 AM, Matt Ingenthron<[email protected]> wrote:
> >
> > I have a USDT provider in memcached which is defined as either a positive
> > value returned or -1 if there is no result. ?From my DTrace script, the
> > value returned seems to be 4294967295 when I'm expecting a -1 so it seems
> > to be treating it as unsigned. ?The value is defined as an int in the USDT
> > probe and the program, and isainfo -b returns 64, though I am working with
> > a 32-bit binary.
> [ ... ]
> >
> > If I add a cast to the script, I get the expected behavior when the probe
> > fires:
> >
> > memcached*::command-*
> > {
> > ?printf("key is %s, length is %d\n", copyinstr(arg1), (signed int) arg3);
> > }
> >
> > Why should this be necessary in this case?
>
> The types for arg0, arg1, etc., are int64_t. In your case, you're
> trying to print a negative 32-bit value, which is a positive 64-bit
> value, thus the need for the cast.
To be more particular, in order to get the types from the provider, you must
use the args[] array, not the arg? variables. Try doing:
printf("key is %s, length is %d\n", copyinstr(arg1), args[3]);
Cheers,
- jonathan
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